Transformer with heat dissipating support means



Fllll lnvean tor' 7 fl/QW/ Him-neg Howavd T. Jones 8 His H. T. JONES Filed March 5,- 1962 TRANSFORMER WITH HEAT DISSIPATING SUPPORT MEANS Dec. 8, 1964 United States Patent 3,160,337 TRANSFQRMER Wi'lfli HEAT G SUE-FURT MEANS Howard Tl". Jones, ersonville, MG, to Gem oral Electric @ompany, a corporation of New Yorlr Filed T's larch 5, F962, Ser. No. lilflflil 8 @laims. (ill. see -er;

This invention relates in general to the field of trans formers and, more particularly, to transformers of the core type wherein a strip of grain-oriented si'con steel is wound to form a ring and primary and secondary coils are placed thereon.

It is well known in transformer designs that substantially all of the losses occurring in transformation of a current are due to an irreversible conversion of electrical energy to heat. The heat thus produced raises the temperature of the core and coil which in general leads to a greater production of heat. if all of the heat were confined to the core and coil and not dissipated, resistivity of the coil could rise to the point where the electrical energy is converted almost entirely in heat. in the normal transformer construction, the heat is dissipated by radiation from the outer surface of the transformer unit. Since the rate at which heat is radiated from the surface is directly proportional to the difference between the temperature of the surface and the surrounding medium, the temperature rise in the transformer is stopped when the temperature thereof is raised sufficiently to increase the radiation rate to the point where the amount of heat radiated is equal to the amount produced in the operation of the transformer. To some extent the effects of conduction and convection also enter into the thermal operation of a transformer in that the heat, of course, is not all produced on the surface of the transformer and, therefore, must be conducted from the interior to the surface to be radiated therefrom and the atmosphere which receives the heat is moved away by convection currents.

Various solutions to the problem of maintaining a transformer at low operating temperatures have been devised previously utilizing forced-air or liquid cooling to aid heat dissipation although such constructions are sometimes costly to manufacture and maintain. Some of the best systems from an economical standpoint are those using the natural forces of radiation, conduction and convection only. It is an object of this invention to provide a transformer having a simple, inexpensive means of improving the heat characteristics of a transformer.

The amount of heat produced varies with the flux density; therefore, one means of reducing the heat characteristic of a transformer is to increase the amount of material in the core. Thus, where the amount of iron is increased, the flux density decreases and the surface area increases so that the temperature rise of the transformer is decreased. Similarly, if the size of the copper wire used is increased, the resistance of the copper is decreased and the heat production is decreased. However, the addition of more material to a transformer is an additional expense and, where cost is extremely important, no excess material can be used economically. Therefore, it is an object of this invention to provide a transformer which does not contain excessive material simply to permit operation at lower temperatures. in other words, for any given transformer presently used, it is an ob'ect of this invention to provide means whereby the size of the transformer may be reduced while still keeping a transformer within allowable thermal limits.

A further object is to provide a transformer which uses a minimum of parts and may be readily resembled.

In accordance with the above objects, there is provided a transformer comprising a core of magnetic material,

" Ice primary and secondary coils around said core, and a heatdissipating support means of substantially non-magnetic material having a section thereof 'uxtapositioned against the core so as to underlie both the primary and secondary coils and another section thereof extending outwardly away from said core, whereby heat may be readily drawn from the interior of the core and coil, conducted through said means and radiated to the external surroundings.

The invention further provides a transformer comprising a magnetic circuit loop formed of a plurality of laminations of magnetic material bent fiatwise and wound layer upon layer to form a closed path about a central Window; a magnetic shunt of at least one flat stack of laminations of magnetic material placed against the side of said circuit loop spanning said window, the laminations of said loop and said shunt being placed in edge-toedge relationship with each other; said loop being provided with a butt joint on one side of said magnetic shunt and with an area of reduced cross section on the other side of said magnetic shunt; a primaryelectrical winding on said loop on said one side of said magnetic shunt and overlying said butt joint; a secondary electrical winding on said loop on said other side of said loop, a heatdissipating support means comprising a generally U- shaped bracket, one of the leg members thereof having therein a slot and being juxtapositioned against the magnetic circuit loop so as to underlie both primary and secondary coils, the bight extending away from the magnetic circuit loop and the other leg thereby being spaced away from the magnetic loop and the winding whereby heat may be readily drawn from the interior of the core and coil, conducted through the heat-dissipating means and radiated to the external surroundings; and a flexible band extending through said slot and around said core.

In accordance with further objects of the invention there is provided a method of manufacturing a transformer comprising a core of magnetic material, primary and secondary coils around said core, and a heat-dissipating support means of substantially non-magnetic material having a section thereof juxtapositioned against the core so as to underlie both the primary and secondary coils and another section thereof extending outwardly away from said core, whereby heat may be readily drawn from the interior of the core and coil, conducted through said means and radiated to the external surroundings which includes the steps of first inserting over a cut section of a strip wound core a secondary coil, and then inserting thereover a primary coil, juxtapositioning a heat-dissipating support means having a slot therein against the core and underlying said primary and secondary coils, butting another section of core material against the first-mentioned section of core, inserting a flexible hand through the slot and around the core sections underneath the coils, and fastening the ends of the band together.

Further objects and advantages shall appear to one skilled in the art from the following specification and description:

FIG. 1 is an isometric view of a transformer constructed in accordance with the invention;

FIG. 2 is a side elevational view of an electrical ballast utilizing a transformer made in accordance with the invention partly in section;

FIG. 3 is a side view of the ballast of FIG. 2; and

FIG. 4- is a modification of a transformer made in accordance with the invention.

As shown in Fl 1, the transformer 5 comprises a core 5, primary and secondary coils 7 and 8 respectively, and magnetic shunts 9 located between the coils. The

transformer 5 includes a heat-dissipating support means ill for locating a transformer with a canister 11 (FIG. 2) to make a complete ballast. The canister 11 may also include capacitors 12 therein held away from the transformer by support means 13. The canister 11 normally contains a potting compound completely surrounding the transformer 5 and is closed by a lid 14.

The core structure of the reactive transformer 5, as shown, comprises the generally rectangular core loop 6 of magnetic strip material wound fiatwise layer upon layer until a suificient cross-sectional area is built up around a center window 15. After winding of the core loop 6, the superimposed laminations 16 may or may not be bonded together by any known technique, e.g. epoxy glue or welding, to prevent their subsequent separation and the loop 6 is then cut into two unequal sections 17 and 18.

Cutting of the core 6 into two sections 1'7 and 18 permits placement thereon of pre-wound coils thus eliminat ing the need for the more expensive process of winding the coil directly on a solid core. After the primary and secondary coils 7 and 8 are assembled thereon, the two sections 17 and 18 of the core loop 6 are fastened together by the use of a flexible band 19, the ends of which band 19 are joined by a clip 20. The butt joints 21 (FIG. 2) formed when the sections are re-assembled together are advantageously used to control the input power factor of the transformer by controlling the width of the joint 21 with an insulating piece 22.

As shown, the primary and secondary coils 7 and 3, respectively, are spacedly positioned on the longer sides of the core 6. The primary coil '7 consists of a pair of copper windings 23 and 24 and the secondary coil consists of a pair of copper windings 25 and 26 which permit a symmetrical placement of the copper around the core 6. The primary and secondary coils may be a single winding, if desired. The windings 23, 24, 25 and 26 are insulated from the transformer core 6 by a layer of insulating material such as the paper insulators 27 shown. The butt joint 21 formed by joining the two unequal sections 17 and 18 of the core loop 6 occurs in that part of the magnetic circuit including the primary windings 23 and Z4 and, as shown in FIG. 2, lies immediately underneath these primary windings. By placing the butt joint 21 in the primary portion of the magnetic circuit, only the primary magnetizing reactance is affected and the effective gap may be adjusted by modifying the size of insulation piece 22 to control the input power factor. The butt joint 21 does not therefore adversely affect the secondary magnetizing inductance and thereby increase losses.

In that larger section 18 of the core loop 6 which is to carry a secondary winding, a restriction 28 in the crosssectional area of the core 6 is introduced to provide a saturable area if the core is being used to provide a regulator ballast. If the core 6 is to be used in a lag ballast, the core need not be provided with a restricted cross-sectional area in the secondary. As shown, however, a narrow slot 29 in the edge of the core is provided to a depth of approximately one-third the width of the laminations.

The loose magnetic shunts 9 consist of a stack of flat generally rectangularly shaped laminations 3th of magnetic material spaced from the core loop 6 by an insulating layer 31. The laminations Sti may be grain-oriented steel with the direction of highest permeability extending longitudinally of the laminations. The laminations 3d are placed beside the core loop 6 in edge-to-edge relationship with the laminations 16 of the loop 6 to span the central window thus providing a leakage path for the primary and secondary portions of the magnetic circuit. This disposition of the magnetic shunts 9 overcomes the problem which, until now, has discouraged the use of strip winding techniques in the formation of reactive transformer cores. It has been customary to place the shunt in the plane of the basic core loop but, if such a shunt were placed within the plane of a strip-wound core, most of the flux shunted through it would necessarily have to pass through several adjacent layers of laminations in the core loop in a direction normal to the laminations before ever entering the shunt, an eventuality that would materially increase core losses and decrease the efliectiveness of the shunt. For this reason as much as any other, the core structure to prior reactive transformers has been generally formed of stack punchings, which, although somewhat wasteful of magnetic material, have had satisfactory electrical characteristics. By placing a laminated shunt beside the wound core loop instead of in the same plane and orienting its laminations edge to edge with those of the core loop, the effectiveness of the shunt is preserved and it becomes feasible to strip wind the core loop. The resulting core structure is therefore very economical because it can be entirely formed of strip material with no appreciable waste. In this connection it should be noted that the shunt laminations 30 may be cut from strip material of the proper width with no waste.

The shunts 9 are secured to the sides of the core 6 between the primary and secondary coils 7 and 8 by fastening means 32. While other methods, such as tacky tape, may be used, as shown, the fastening means 32 is a sleeve 33 of insulating material such as paper made by stapling the ends of a strip together. The shunts 9 are then securely held against the core by inserting a small wedge 34 between the sleeve and one of the shunts.

Since the primary and secondary coils, together with the shunts, almost entirely enclose the strip-wound core, the heat energy created by the iron losses and the copper losses is radiated only from the exposed ends of the stripwound core and the outer surfaces of the primary and secondary coils. Therefore, the heat developed in the area located between the core and coils tends to build up hot spots in the interior and the losses are increased thereby because of the increased resistance of the coils. The increase of heat may cause early breakdown of the insulation and shorting out of the windings. The heatdissipating support means 10 provides a thermal-conducting path for the heat to be taken away from the interior of the transformer to eliminate the hot spotting. The heat-dissipating means It? is placed between the coil and core so as to most efficiently perform its function. If a heat exchanger were attached to the ends of the core, the heat created in the interior would still have to be conducted by the core itself away from the interior. The heat-dissipating support means 10 as shown in FIGS. 1-3 is a generally U-shaped bracket with one leg 35 juxtapositioned against the strip-wound core 6 and underlying the coils 7 and 8 and the other leg 36 lying parallel thereto exterior of the coils 7 and 8 and spaced therefrom so as to provide a large radiating surface from which to dissipate the heat created by transformer operations. To provide a larger radiating surface, the outer leg 36 may be provided with wings 37. The two legs are connected by a bight 38 which provides a good thermal-conducting path for the heat and a base on which the transformer is supported in an erect position in canister 11. In the leg 35 lying next to the strip-wound core, a slot 39 is punched whereby the band 19 may be threaded therethrough and the heat-dissipating means 10 assembled with the core sections 17 and T8 in a single operation, thus no extra fastening means is necessary to attach the heat-dissipating means.

In the modification shown in FIG. 4, wherein the transformer 5 is to be merely mounted on a wall or pole support in a covered area where it is not necessary to enclose it, the heat-dissipating support means 10' may take a modified form. This support comprises a generally U- shaped bracket with the bight 38' extending entirely along the side of the core 6 and underlying the primary and secondary coils 7 and 8. The legs 35' and 36' extend outwardly away from the transformer and the extremities of the legs are provided with extensions 40 whereby the bracket may be attached to some supporting body. For example, the outer extensions may be provided with holes or slots through which screws may be inserted to attach arouse? the transformer to a wall. The extensions might also be used without slots or holes if proper clamps were used to hold the heat-dissipating support means. In some instances, the outer extremities may be used to support the transformer in a suitable channel-shaped member in which it may be slidably inserted. Slots 39 are provided in bight 38' whereby the band 19 may be threaded there through and the heat-dissipating support means 10' assembled with core sections 17 and 18 in a single operation.

The heat-dissipating support means 1t is made of aluminum because of its high thermal conductivity and low magnetic characteristics. The aluminum heat-dissipating means has a higher thermal-conductivity characteristic than the copper or the iron in which it is in close proximity and, thus, the leg 35 lying within the interior of the transformer acts as a heat sink to which the heat is attracted. From this leg 35, the heat is conducted through the bight to the outer leg 36. Preferably the outer leg 36 is made with a larger area than the interior leg 35 so as to provide a larger surface area from which to radiate the heat to the surrounding atmosphere, to give the heat sink a chimney effect since the neat naturally travels from the hotter part of the heat-dissipating means 10 to the part which is being constantly cooled by the surrounding atmosphere. Since the aluminum has very low magnetic permeability, it has very little influence on the magnetic characteristics of the transformer.

From the above description the transformer provided is one which may be readily manufactured in the following manner: the core 6 may be Wound on a standard winding machine and then cut into unequal sections 17 and 18. The slot 29 may be sawed in the larger core section 18. Precision windings 25 and 26 may be slipped over the legs of section 18 to provide the secondary for the transformer. Precision windings 23 and 24 are then slipped over section 18 to form the primary coil. After juxtapositioning the heat-dissipating support means 10 against the sides of the core underlying primary and secondary coils 7 and 8, the small section 17 of the core is butted against section 18 and the band 19 is inserted through the slots 29 and around the core sections. After tensioning of the band 19, the sealing clip 20 is secured to its ends to secure the assembled structure together. The primary coil '7 and the secondary coil h is then slid to opposite ends of the window 15 and the sleeve 33 inserted through the window. Magnetic shunts 9 are inserted into sleeve 33 on either side of the core so that laminations 30 thereof are in edge-to-edge relationship with laminations 16 of the core. The wedge 34 is then inserted between one of the shunts 9 and a part of sleeve 33 so as to firmly secure the shunts in place on the core. If desired, packings 41 may be inserted in the extremities of the window 15 so as to more securely hold the coils in place. As thus far stated, the above procedure would be followed for the transformer shown in FIGS. 1-3 as well as that shown in FIG. 4. To make a complete ballast as shown in FIGS. 2 and 3, it is only necessary to insert the transformer into a canister 11 together with the necessary capacitors, fill the canister with potting compound and seal the lid 14 thereon.

While the invention has been specifically disclosed and shown in the accompanying drawings, it will be apparent to one skilled in the art that changes may be made without departing from the spirit of the invention as defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A transformer comprising a magnetic circuit loop formed of a plurality of laminations of magnetic material wound layer upon layer to form a closed path about a central window; a magnetic shunt of at least one fiat stack of laminations of magnetic material placed against the side of said circuit loop spanning said window, the

laminations of said loop and said shunt being placed in edge-to-edge relationship with each other; said loop being provided with a butt joint on one side of said magnetic shunt and with an area of reduced cross section on the other side of said magnetic shunt; a primary electrical winding on said loop on said one side of said magnetic shunt and overlying said butt joint; a secondary electrical winding on said loop on said other side of said loop, a heat-dissipating support means comprising a generally U-shaped bracket, one of the leg members thereof having therein a slot and being juxtapositioned against the magnetic circuit loop so as to underlie both primary and secondary coils, the bight extending away from the magnetic circuit loop and the other leg thereby being spaced away from the magnetic loop and the winding whereby heat may be drawn from the interior of the core and coil, conducted through the heat-dissipating means and radiated to the external surroundings; and a flexible band extending through said slot and around said core.

2. A transformer comprising a core of magnetic material, primary and secondary coils around said core, and means whereby heat may be readily drawn from the interior of the core and coil, conducted through said means and radiated to the external surroundings including a support means of high thermal conducting material having a section thereof juxtapositioned against the core so as to underlie both the primary and secondary coil and another section thereof extending outwardly away from said core.

3. A transformer comprising a core of magnetic material, primary and secondary coils around said core, and means whereby heat may be readily drawn from the interior of the core and coil, conducted through said means and radiated to the external surrounding including a generally U-shaped bracket of high thermal conducting material having one of the leg members thereof juxtapositioned against the core so as to underlie at least one of the coils and the other leg thereof being spaced away from the core.

4. A transformer comprising a magnetic circuit loop for-med of a plurality of laminations of magnetic material wound layer upon layer to form a closed path about a central window, a magnetic shunt of at least one flat stack of laminations of magnetic material placed against the side of said circuit loop spanning said window, the laminations of said loop and said shunt being placed in edgeto-edge relationship with each other, said loop being provided with a butt joint on one side of said magnetic shunt and with an area of reduced cross section on the other side of said magnetic shunt, a primary electrical coil on said loop on said one side of said magnetic shunt and overlying said butt joint, a secondary electrical winding on said other side of said loop, and a heat-dissipating support means comprising a generally U-shaped bracket having one of the leg members being juxtapositioned against the magnetic circuit loop so as to underlie at least one of said electrical coils.

5. A transformer comprising a magnetic circuit loop formed of a plurality of laminations of magnetic material wound layer upon layer to form a closed path about a central window, a magnetic shunt made of two flat stacks of laminations of magnetic material placed against the side of said circuit loop spanning said window, the laminations of said loop and said shunt being placed in edge-to-edge relationship with each other, means for securing said shunt to said magnetic circuit loop comprising a loop of flexible material extending through said window and around each of the stacks of laminations, primary and secondary electrical coils spaced on said core and a heat-dissipating support means of high thermal conducting material having a section thereof juxtapositioned against the core so as to underlie at least one of the coils and another section thereof extending outwardly away from said core whereby heat may be readily drawn 5 from the interior of the core and coil, conducted through said means, and radiated to the external surroundings.

6. A ballast comprising a canister containing a capacitor and transformer surrounded by suitable potting compound, said transformer comprising a core of magnetic material, primary and secondary coils around said core, and a heat-dissipating support means of high thermal conducting material, having a section thereof juxtaposed against the core so as to underlie both the primary and secondary coils, and another section juxtapositioned against the Wall of said canister whereby heat may be readily drawn from the interior of the core and coil, 0on ducted through said means and radiated to the walls of the canister.

7. A ballast as defined in claim 6 wherein said other section of the heat-dissipating support means is provided With wing extensions whereby a greater heat-radiating surface is provided.

8. A ballast comprising a canister containing a transformer surrounded by suitable potting compound, said transformer comprising a core of magnetic material, primary and secondary coils around said core, and a heatdissipatingsupport means of high thermal conducting material, having a section thereof juxtaposed against the core so as to underlie both the primary and secondary 8 coils, and another section juxtapositioned against the Wall of said canister whereby heat may be readily drawn from the interior of the core and coil, conducted through said means and radiated to the walls of the canister.

References Qited in the file of this patent UNETED STATES PATENTS 1,385,624 Kent July 26, 1921 1,849,376 Morse Mar. 15, 1932 2,114,189 Kronmiller Apr. 12, 1938 2,220,615 Pittman et al. Nov. 5, 1940 2,318,095 Putman May 4, 1943 2,343,725 Wilson Mar. 7, 1944 2,431,189 Moreton et a1 Nov. 18, 1947 2,464,029 Ehrrnan Mar. 8, 1949 2,514,015 Sutter July 4, 1950 2,586,320 Ford Feb. 19, 1952 2,771,587 Henderson Nov. 20, 1956 2,825,034 Birchard Feb. 25, 1958 2,930,012 Hufnagel Mar. 22, 1960 2,947,957 Spindler Aug. 2, 1960 FOREIGN PATENTS 186,321 Austria Oct. 15, 1955 1,232,044 France Oct. 5, 1960 

1. A TRANSFORMER COMPRISING A MAGNETIC CIRCUIT LOOP FORMED OF A PLURALITY OF LAMINATIONS OF MAGNETIC MATERIAL WOUND LAYER UPON LAYER TO FORM A CLOSED PATH ABOUT A CENTRAL WINDOW; A MAGNETIC SHUNT OF AT LEAST ONE FLAT STACK OF LAMINATIONS OF MAGNETIC MATERIAL PLACED AGAINST THE SIDE OF SAID CIRCUIT LOOP SPANNING SAID WINDOW, THE LAMINATIONS OF SAID LOOP AND SAID SHUNT BEING PLACED IN EDGE-TO-EDGE RELATIONSHIP WITH EACH OTHER; SAID LOOP BEING PROVIDED WITH A BUTT JOINT ON ONE SIDE OF SAID MAGNETIC SHUNT AND WITH AN AREA OF REDUCED CROSS SECTION ON THE OTHER SIDE OF SAID MAGNETIC SHUNT; A PRIMARY ELECTRICAL WINDING ON SAID LOOP ON SAID ONE SIDE OF SAID MAGNETIC SHUNT AND OVERLYING SAID BUTT JOINT; A SECONDARY ELECTRICAL WINDING ON SAID LOOP ON SAID OTHER SIDE OF SAID LOOP, A HEAT-DISSIPATING SUPPORT MEANS COMPRISING A GENERALLY U-SHAPED BRACKET, ONE OF THE LEG MEMBERS THEREOF HAVING THEREIN A SLOT AND BEING JUXTAPOSITIONED AGAINST THE MAGNETIC CIRCUIT LOOP SO AS TO UNDERLIE BOTH PRIMARY AND SECONDARY COILS, THE BIGHT EXTENDING AWAY FROM THE MAGNETIC CIRCUIT LOOP AND THE OTHER LEG THEREBY BEING SPACED AWAY FROM THE MAGNETIC LOOP AND THE WINDING WHEREBY HEAT MAY BE DRAWN FROM THE INTERIOR OF THE CORE AND COIL, CONDUCTED THROUGH THE HEAT-DISSIPATING MEANS AND RADIATED TO THE EXTERNAL SURROUNDINGS; AND A FLEXIBLE BAND EXTENDING THROUGH SAID SLOT AND AROUND SAID CORE. 